The present application relates to a planar illumination device performing large surface emission by successively arranging a plurality of unit light guide plates.
In recent years, liquid crystal display panels, advertising panels for indoor and outdoor uses, signboards and the like become larger, and accordingly, thinner and larger planar illumination devices as backlights of these apparatuses are necessary. To achieve a thinner planar illumination device, for example, a light guide plate including a first light guide section and a second light guide section which is thinner than the first light guide section and has a surface recessed toward an emission surface on a side opposite to an emission surface is formed. For example, as described in Japanese Unexamined Patent Application Publication No. 2009-37744, there is proposed a method of arranging a base plate in a recession part recessed toward the emission surface of the second light guide section, and containing the light guide plate and the base plate in a frame made of a thin metal plate. Thereby, a balance between a reduction in profile of the light guide plate and rigidity of a liquid crystal panel is achievable.
With regard to upsizing of a light guide plate, it is difficult to form one large light guide plate, and the cost of forming the large light guide plate is high. Therefore, a method of forming a large surface light source by successively arranging a plurality of unit light guide plates is considered. In this method, the large surface light source is manufactured more easily than a method using a large light guide plate, and cost reduction is achievable. However, in the case where a plurality of light guide plates are successively arranged to form a large surface light source, when the large surface light source emits light, a very small amount of illumination light is leaked from a connection section between the light guide plates to cause scattering in a boundary surface, thereby a bright line may be generated in the connection section.
As one technique for solving such an issue, for example, as described in Japanese Unexamined Patent Application Publication No. 2007-213951, there is proposed a technique in which thin ends which are connection parts of unit light guide plates are formed in a recessed-and-projected shape, and a diffusion sheet is arranged on the unit light guide plates, thereby a bright line leaked from a gap between the connection parts is dispersed.